The present invention relates generally to automotive service equipment designed to measure imbalance in a vehicle wheel assembly, and in particular, to an improved vehicle wheel balancer system configured to identify an amount of imbalance correction weight for application to a vehicle wheel which is sufficient to reduce imbalances in the vehicle wheel below an imbalance correction threshold level.
Wheel balancer systems are designed to determine imbalance characteristics of a rotating body such as a wheel assembly consisting of a wheel rim and a pneumatic tire, or of a wheel rim alone. The determined characteristics include, but are not limited to static imbalances (i.e., “shake” forces), dynamic imbalances (i.e., couple or “shimmy” forces), lateral forces, radial forces and runout parameters. Determination of some of these characteristics result from direct measurements, while others are obtained from an analysis of the mechanical vibrations caused by rotational movement of the rotating body. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers mounted in the wheel balancer system, which are configured to convert the mechanical vibrations into electrical signals.
Additionally, it is important to provide an operator with information about whether or not there is a need to correct a detected imbalance in the wheel rim or wheel assembly, or if the detected imbalance is sufficiently small so as to have a negligible effect on vehicle performance and handling, i.e., below an imbalance correction threshold level. When there is a need to correct a detected imbalance in a vehicle wheel, current vehicle wheel balancer systems are designed to calculate the size and placement positions for one or more imbalance correction weights. The imbalance correction weights are typically made from lead, which is known to have toxic effects on the environment, or from zinc, which is less toxic than lead, but which is more expensive. Those of ordinary skill of the art will recognize that other materials may also be used for imbalance correction weights.
Current vehicle wheel balancer systems are configured to calculate a sufficient amount of imbalance correction weight to reduce the detected imbalance in the vehicle wheel assembly to near zero. Wheel rim sizes on the market range from 12.0 inches in diameter up to at least 28.0 inches in diameter. It is anticipated that wheel rim sizes will increase to 30.0 inches and beyond in diameter in the future, with a corresponding increase in associated tire sizes. Due to the limited size increments in which imbalance correction weights are available, conventional vehicle wheel balancer systems are configured to display, as a zero value, any required imbalance correction weight amounts below the threshold associated with the smallest incremental weight size. Typically this weight threshold is selected to be slightly greater than the smallest standard incremental imbalance correction weight size, regardless of the size of the wheel rim or wheel assembly. Conventionally, imbalance correction weights are produced in increments of 0.25 ounces for English units, and 5.0 grams for metric units.
This can result in an operator “chasing” weights on a small or narrow wheel due to the significant effect of the threshold level on imbalances, and a poor balance on larger diameter wheels due to a reduced effectiveness of the threshold level. One solution is shown in U.S. Pat. No. 6,484,574 to Douglas, in which a balancer is configured to select the best weight plane locations from data acquired by scanning the rim profile. This is an advantageous method, but it is not economical for all balancers to have this feature.
Clearly, it would be advantageous to provide a vehicle wheel balancer system with a method for determining an imbalance threshold level at which imbalance correction is required for a vehicle wheel, and which is independent of the dimensions of the wheel assembly undergoing balancing or the incremental size of the imbalance correction weights employed, and which optionally provides an operator with a scaled visual indication of any imbalances present relative to the determined imbalance threshold level.
It would be further advantageous to provide a vehicle wheel balancer system with a method for reducing the amount of imbalance correction weight utilized to correct an imbalance measured in a vehicle wheel assembly, thereby either reducing the amount of lead weights introduced into the environment, or resulting in a corresponding cost savings through a reduction in the total applied weight amounts.